β-sialon containing Eu2+ in a solid solution is an oxynitride phosphor having β-sialon represented by the general formula Si6-zAlzOzN8-z (where z is larger than 0 and no more than 4.2) as a host crystal, and containing Eu2+ in a solid solution as an emission center, which is excited by UV-to-blue light and emits green light in the 520 to 560 nm range (Patent Document 1). Eu2+-activated β-sialon phosphors have little decrease in luminance with temperature increases, and have excellent durability, and are therefore widely used as green-light-emitting phosphors for use in light-emitting diodes (hereinafter referred to as LEDs) in light-emitting devices.
When mounting such a phosphor in a light-emitting device, the phosphor is generally dispersed in a light-transmitting sealing resin such as an epoxy resin, a polycarbonate or a silicone rubber to form a slurry, and this slurry is applied so as to surround the light-emitting element on the light-emitting surface and cured.
However, conventional β-sialon phosphors do not have adequate wettability with sealing resins and therefore have low adhesion to sealing resins, so that in some cases, separation can occur at the interface between the phosphor and the sealing resin. Since separation at the interface causes refraction or scattering of light, the accumulation of separation at the interface with a sealing resin over time can cause reduced luminance and color shift. For this reason, there were problems in that, even if the β-sialon phosphor itself has excellent heat resistance and durability, the properties thereof were difficult to fully realize, and long-term stability could not be achieved.